The invention concerns flame holder devices for combustion chambers traversed by a flow of combustible gases. It concerns more particularly a flame holder device of the type used in the combustion chambers of aircraft turbojet engines and specifically in the after burner tubes of afterburning turbojet engines equipped with a reheating system.
It is known to equip the afterburning turbojet engines of commercial aircraft with a partial reheating system operating in the afterburner tube, either by increasing the rate of flow of the bank of injectors of the tube, or by the activation of supplementary injectors in order to compensate for an insufficiency of thrust due to the failure of an engine during takeoff by means of an instantaneous increase in the rate of reheating of the intact engines.
The afterburner tube of each engine is normally equipped with a flame holder ring arranged downstream from fuel injectors. In anticipation of the modification of the normal operating mode as the result of the intervention of the partial reheating system, it is known to increase the useful surface of the flame holder ring by means of flame holder arms secured to the ring and arranged so as to radiate from said ring. The following devices are known:
(a) to render the flame holder ring optimally effective, its cross section is advantageously of a U or V shape, with the sides joined by an arch with each spine oriented in the downstream direction of flow, PA1 (b) similarly, the transverse cross section of each flame holder arm is also in the shape of a U or V, with their sides joined by an arch facing with its spine in the downstream of flow, PA1 (c) in order to prevent the overheating of the wall of the tube due to the proximity of the end of the arms fastened to the external flank of the ring (i.e. the side facing the wall), it is preferred that at least the diameter of the ring should not be very much smaller than that of the tube and to secure the arms to the internal side of the ring, from where they radiate in the direction of the axis of the tube. PA1 the cross section of each arm evolves so that the dihedron constituted by the sides becomes more open as the section approaches the ring. In this manner, the drag on each arm is reduced appreciably and the center of thrust located in the vicinity of the ring; PA1 the end of each arm opposed to the remote end is closed by a plate which facilitates its cooling by means of convective and radiative effects and all of the plates of the plurality of arms are oriented so that they define a conical surface with its apex facing upstream of the ring, in such manner that the incidence of the plates in relation to the flow eliminates separations harmful to the efficiency of cooling.
Without it being necessary to resort to the latter arrangement, it may be stated that it further presents the advantage that it generates at the outlet of the blast pipe of the tube a core of hot gas extending downstream from the outlet and wherein combustion may continue; this contributes to a decrease in the emission of unburned matter.
Whether the arms are fastened to the inner or the outer flank of the ring, it is customary to secure them by means of welding and to arrange the arms so that the weld will have the greatest length possible for the obvious reason of obtaining maximum mechanical strength and rigidity of the ring and arm assembly.